linux-kernel - Re: [PATCH v11 20/20] x86/cpu/amd: Do not print FW

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Message-ID: <CALMp9eRZtg126iSZ4zzH_SjEz2V+-FRJfkw7=fLxSoVL1NTp_g@mail.gmail.com>
Date: Fri, 13 Sep 2024 10:42:13 -0700
From: Jim Mattson <jmattson@...gle.com>
To: Nikunj A Dadhania <nikunj@....com>
Cc: linux-kernel@...r.kernel.org, thomas.lendacky@....com, bp@...en8.de, 
	x86@...nel.org, kvm@...r.kernel.org, mingo@...hat.com, tglx@...utronix.de, 
	dave.hansen@...ux.intel.com, pgonda@...gle.com, seanjc@...gle.com, 
	pbonzini@...hat.com
Subject: Re: [PATCH v11 20/20] x86/cpu/amd: Do not print FW_BUG for Secure TSC

On Wed, Jul 31, 2024 at 8:16 AM Nikunj A Dadhania <nikunj@....com> wrote:
>
> When Secure TSC is enabled and TscInvariant (bit 8) in CPUID_8000_0007_edx
> is set, the kernel complains with the below firmware bug:
>
> [Firmware Bug]: TSC doesn't count with P0 frequency!
>
> Secure TSC does not need to run at P0 frequency; the TSC frequency is set
> by the VMM as part of the SNP_LAUNCH_START command. Skip this check when
> Secure TSC is enabled
>
> Signed-off-by: Nikunj A Dadhania <nikunj@....com>
> Tested-by: Peter Gonda <pgonda@...gle.com>
> ---
>  arch/x86/kernel/cpu/amd.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
> index be5889bded49..87b55d2183a0 100644
> --- a/arch/x86/kernel/cpu/amd.c
> +++ b/arch/x86/kernel/cpu/amd.c
> @@ -370,7 +370,8 @@ static void bsp_determine_snp(struct cpuinfo_x86 *c)
>
>  static void bsp_init_amd(struct cpuinfo_x86 *c)
>  {
> -       if (cpu_has(c, X86_FEATURE_CONSTANT_TSC)) {
> +       if (cpu_has(c, X86_FEATURE_CONSTANT_TSC) &&
> +           !cc_platform_has(CC_ATTR_GUEST_SECURE_TSC)) {

Could we extend this to never complain in a virtual machine? i.e.
...
-       if (cpu_has(c, X86_FEATURE_CONSTANT_TSC)) {
+       if (cpu_has(c, X86_FEATURE_CONSTANT_TSC) &&
+           !cpu_has(c, X86_FEATURE_HYPERVISOR)) {
...